Unfortunately, Dave, much of the Galatians corpus has not been Englished. However, some of the good Reformed material in English would include William Perkins (as noted above, and this may perhaps be one of the finer works of any nationality, though you may find therein more than you were seeking), James Fergusson, and David Dickson. Also, if you can obtain a copy (it is freely available online in the complete edition of his works), Thomas Boston's paraphrase is superb. Jean Calvin is, of course, more than worth reading. And though the section on Galatians is not the high point of the production, you might find the English (Westminster) Annotations useful. Coming from a bit later period, John Brown of Edinburgh's work is very good.